What makes a bird a bird? Shared ancestral character: a trait that is found in the ancestor of a group and all of the derived taxa have the trait common ancestor for all taxa at root of the tree Critical innovations = Shared Derived Character adaptive traits that define new taxa marked with ‘slashes’ on tree evolutionary novelties to distinguish taxa
Principle of Parsimony = Simplest solution is the likely path of evolution A logical way to identify homologous and analogous traits Minimize the # of evolutionary changes needed to explain your character data
Phylogenetic trees based on morphology place whales outside of the artiodactyl group Artiodactyl mammals = cows, deer and hippos hooves with even number of toes unusual pulley-shaped ankle bone Astragalus ankle bone is a shared derived trait for all artiodactyls the principle of parsimony, based on this trait, should exclude whales
How do we determine evol’n relationships? morphology - presence/absence of ankle bone DNA sequences - shared gene families Depends on what data you have! poor fossil records made this tricky Modern genetic data now suggests a closer relationship between whales and hippos…